1 August 2020 | New Scientist | 43the benefits are far more significant than this
alone. He makes the case that even if there is
no obviously harmful mutation, women tend
to be at an advantage by having bodies made
up of two populations of genetically different
cells, and that this begins even before birth.
He believes this is the reason why women are
less vulnerable to certain congenital disorders
and better at fighting off infections –
including the coronavirus. As he sees it,
women are simply genetically superior.
Having two copies of an X chromosome has
far more benefits than we realised, and
serious implications for medicine.Clare Wilson: How can women be the
stronger sex, when we are generally
smaller and physically weaker?
Sharon Moalem: All those things are true –
on average, males have more muscle mass.
But I am talking about genetic superiority,
and the parameter is survival. We see the
consequences in many areas of medicine.
When you look at supercentenarians, those
over the age of 110, they are 95 per cent female.
But it isn’t just making it to old age –females have a survival advantage over
the life course. When I was a physician at a
neonatal intensive care unit, I saw that more
girls make it to their first birthday than boys.
And I was seeing lower rates of congenital
malformations like tongue-tie and clubfoot.
Anything that’s biologically difficult to form,
females do better.How is this connected to the X chromosome?
Because there are about a thousand genes
on the X. Mammalian females have two
populations of cells that are active within
them; they are really mosaics in this way.
Males have just one copy of the X so they
aren’t mosaics. In females, those two
populations build their bodies during fetal
life. They cooperate and share not just genetic
materials with one another, but proteins and
enzymes, which give extra ability to handle
disease. While the embryo is developing,
you have an immense amount of cell
multiplication where cells grow and divide
into two, so the cells that have a growth
advantage will be the ones that dominate in
RO that tissue. Even in tissues that are initially
CIO
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>W
OMEN generally outlive men
and are less susceptible to certain
illnesses – including covid-19, it
now appears. Why health outcomes are so
drastically different between the sexes is
unclear. But Sharon Moalem, a doctor
and genetic researcher based in New York,
thinks he has the answer. It isn’t because
women tend to go to the doctor more or
have healthier habits, he says. Instead, it’s
because they are typically better equipped,
genetically speaking.
In humans, sex is largely determined by
chromosomes, the bundles of tightly coiled
DNA that carry our genes. The cells of most
women possess two X chromosomes while
most men have one X and one Y. So that
women’s cells don’t have to carry two
versions of each gene on the X chromosome,
one from each X, one of the Xs is mainly
switched off. It appears that which one stays
active in which cells is chosen seemingly at
random some time during the first few weeks
of pregnancy. The result is that half a women’s
cells generally use the X chromosome she
inherited from her mother, while the other
half use the one from her father.
It has long been known that if one X has
a harmful mutation, cells that use the other
X can compensate. That’s why, for instance,
women are less likely to be colour-blind; a
gene important for eye function resides on
the X chromosome. Yet Moalem argues that